Preheat the oven to 350 degrees F. Spread the nuts out in one layer on a baking sheet and bake them, stirring occasionally, until they are well browned, 10 to 13 minutes (they will smell toasted and nutty). Transfer the pan to a wire rack to cool.

In a food processor, grind the nuts with ¼ cup of the flour. Set aside.

Using an electric mixer, beat the butter and sugar until creamy and smooth, about 2 minutes. Add the vanilla and beat well. Sift together the remaining 1 ¾ cups of flour, the salt, and the baking powder, and add it to the dough, mixing until just combined. Stir in the nut mixture. Form the dough into a disk, wrap in plastic wrap, and chill for at least 3 hours.

Preheat the oven to 325 degrees F. Roll the dough between two sheets of wax paper to 3/16 inch thick (a rectangle approximately 10 x 14 inches). Using a sharp knife, cut the dough into 1-inch squares, then cut the squares on a diagonal into triangles (I skipped the last cut into triangles). Sprinkle the cookies with the turbinado sugar. Place them 1 inch apart on ungreased cookie sheets (do not reroll the scraps). Prick the cookies with a fork and bake until pale golden all over, about 10 to 12 minutes. Cool on a wire rack.